If the human element had been at work (maintenance!!) then who knows what gremlins have been introduced into the system? Best way to find out? ...... test the float system ....... best way not to be hurt if said gremlin has been introduced into the system? .... stand clear when I test them please.
At this point I want to say 'simple' just like the meercat on the TV. .... with a funny little noise at the end.
(apologies for non-UK TV viewers).
G.
